Digital display generators

ABSTRACT

A digital display generator generates deflection signals for operating on the deflection circuitry of a display device to move a visual representation, such as a spot generated by the display device, along X and Y axes. A pulse generator is provided to produce pulses at rates representative of the desired rates of movement of the spot in X and Y directions, and counter means is provided for establishing a count representative of the position of the spot along the X and Y axes. Control means is provided for selectively increasing or decreasing the count in the counter means in accordance with the intended direction along the X and Y axes, and converter means is provided for converting the counts to analog signals. Preferably, offset counter means is provided for determining whether or not the intended display is on or off screen, and means is provided for stepping the offset counter in such a manner that when the intended display reaches the region of the screen, the display device is operated to generate the visual representation. In accordance with one aspect of the present invention, a character display generator is provided having storage means containing data relating to each of a plurality of strokes for each of a plurality of characters, and means is provided for addressing the storage means whereby a stroke generator will generate digital signals representative of each stroke of a selected character. Means is provided for advancing the storage means to each successive stroke of the character.

llnited States Patent i191 Erickson et a1.

[11] 3,821,727 1 June 28, 1974 DIGITAL DISPLAY GENERATORS [75] Inventors: Fred W. Erickson, Northridge; John G. Price, Granada Hills, both of Calif.

[73] Assignee: Litton Systems Inc., Beverly Hills,

Calif.

[22] Filed: Apr. 27, I972 [211 App]. No.: 248,042

[52] US. Cl. 340/324 A, 315/18 [51] Int. Cl. G08b 5/36 [58] Field of Search 340/324 A; 315/18 [56] References Cited v UNITED STATES PATENTS 3,329,948 7/1967 Halsted 340/324A 3,637,997 1/1972 Petersen 340/324 A X 3,696,394 10/1972 Kashio, 315/18 X 3,713,134 1/1973 Chaney 340/324 A Primary Examirier-David L. Trafton [57] ABSTRACT A digital display generator generates deflection signals for operating on the deflection circuitry of a display device to move a visual representation, such as a spot generated by the display device, along X and Y axes. A pulse generator is provided to produce pulses at rates representative of the desired rates of movement of the spot in X and Y directions, and counter means is provided for establishing a count representative of the position of the spot along the X and Y axes. Control means is provided for selectively increasing or decreasing the count in the counter means in accordance with the intended direction along the X and Y axes, and converter means is provided for converting the counts to analog signals. Preferably, offset counter means is provided for determining whether or not the 1 intended display is on or off screen, and means is provided for stepping the offset counter in such a manner that when the intended display reaches the region of the screen, the display device is operated to generate the visual representation. In accordance with one aspect of the present invention, a character display gen- 22 Claims, 8 Drawing Figures swap [NABLE x 52557 /2 ,/0 -/a Z7 32 mam/am 7 XRATE i 1 70 M050 CO/VMOA 5/1/4515 COUN7'ER Ml/U/PL/Ek W l M 30 COUNTER 39 LINE 7 x4x/5 37 ASA/67H mm ADVANCE 04 m 52 r /r 70 Lam/Aye Zm/e .W 5/1 4545 alm/m2 CONVERTER is X PUSH-IONS! 70 2 AXIS .co/vr/am Ypaslr/o/v zaa ffjfl 1 42 53, #4625 g 5/ f D/SflAAYB/T 2 42 7'0 YflffZfCf/O/V 4 M752 (Oi/V6275? J4 i 23- 4a CLOCK 2 247 4? um: QA TE YRATE OFFSfT mm (0/1 7204 5/1/4515 CONTEOL tWAELE MUM/ k 1 Coy/WE? l 4/: Y AXIS v OFFSET [24 T5 mm ADVANCE 04m 04 T4 1 DIGITAL DISPLAY GENERATORS This invention relates to digital display generators, andparticularly to digital display generators for generating deflection signals for operating on deflection circuitry of a display device, such as a'cathode ray tube.

Heretofore, generation of deflection signals for cathode ray tubes and the like, has been accomplished by analog circuitry, such as analog voltages formed by ramp generators which produce ramp voltages equal for all deflections. The ramp is attenuated by an attenuator for each axis to thereby proportion the deflection rates for each axis. One problem with such analog generation resides in the fact thatthe gains of the position and line circuitry must be matched in order to assure closure of the line. I A a It isan object of the present invention to provide digital deflection circuits for generation of deflection signals for a display device.- v

It is yet another object of the present invention to provide a display generator for generating deflection.

signals to continuously bias the deflection circuits of a display device to track a visual representation of tracked object.

Another object of the :present invention is to provide display apparatus for displaying visual representations of tracked objects in which thedisplay apparatus is intended to display visual representations of objects in selected sectors of a region, and means is'provided for biasing the deflection circuits of the display apparatus to track the position of objects in all sectors and to operate the video'circuitry when such. objects enter the selected sectors.

Yet another object of the present invention resides in the provision of digital circuitry for generation of character display signals.

' A display generator according to the present invention comprises pulse generator means adaptedto generator pulses at rates representative of the rate of movement of a visualrepresentation along each of two mutually perpendicular axes. Pulse counter means provides for-selectively increasing or decreasing counts representative of the position of the visual-representation along the two axes, the rates of change being dependent upon the respective rates of pulses from said pulse generator means, and the selection of increase or decrease in counts being dependent upon selected positive or negative rnovement of the visual representation along the two axes. Converter means is provided for converting the counts to analog signals for operation on the deflection circuitry of the display device.

One feature of the present invention resides in the provision of offset counter means adapted to sense whether or not a particular visual representation is within a quadrant defined by the screen of the display In accordance with yet another feature of the present storage means containing information relating to a plurality of strokes for each of aplurality of characters. Address means is provided for addressing the storage means, and stroke generator means is provided for generating digital signals representative of each of the strokes required for a display of a character.

The above and other features of this invention will be more fully understood from the following detailed description and the accompanying drawings, in which:

FIG. 1 is a block circuit diagram of a display generator in accordance with the presently preferred embodiment of the present invention;

- FIGS. 2-5 are illustrations representative of the operplay generator in accordance with the presently preferred embodiment of the present invention; and

I FIGS. 7-8 are illustrations of the operation of the apparatus illustrated in FIG. 6. With reference to FIG. 1, there is illustrated a display generator according to the presently preferred embodiment of the present invention having a first digital counter 10 having a plurality of inputs 11 adapted to receive binary information, concerning the length of a line to be displayedfOther inputs to counter 10 include a-sweepenable input 12, a start of line (SOL),input 13, and an enable input 14. The output fromcounter 10 is forwarded through channel 15 to X rate multiplier 16. X rate multiplier 16 has a plurality of inputs 17 adapted to receive X axis advancedata and has an enable input 18. Y

- Line rate control 19, which is a binary multiplier, has a plurality of inputs 20adapted to receive binary data relating to the rate at which lines are to be swept. Enable input 21 and clock input 22 are provided to control 19. Control 19 providesan output via channel 23 to Y rate multiplier 24, to line length counter 10, and to X rate multiplier 16. Y rate multiplier 24 has a plurality of inputs 25 adapted to receive binary data concerning Y axis advance and has an enable input 26. In

addition, the output from line length counter 10 is connected to an input of Y rate multiplier 24. As shown in FIG. 1, channel 15 may also be connected to a Z axis control, if provided.

X rate multiplier 16 provides clock outputs via channel 27 to offset counter 28 and to display bit counter 29. In addition, and as will be more fully understood hereinafter, a sign bit is included in the data loaded into multiplier 16 which is forwarded via channel 30 to offset counter 28 and to Exclusive OR gate 31. Offset counter 28 has a plurality ofinputs 32 for loading offset data into the offset counter. Offset counter 28 includes an output 33 to a second input of Exclusive OR gate 31. The output from Exclusive OR circuit 31 is connected to an input of display bit counter 29.'Counter 29 includes a plurality of inputs 34 adapted to receive X position data and includes an enable input 35. An output 36 from display bit counter 29 provides an advance input to offset counter 28. Digital display data from display bit counter 29 is processed through channel 52 to digital-to-analog converter 37 which, in turn, provides an analog signal via channel 38 to the deflection circuits of a cathode ray tube (not shown). Preferably,

and as will be more fully understood hereinafter, an enable control is provided via channel 39 to the video control of the CRT from offset counter 28.

Similarly, the Y rate multiplier 24 provides clock outputs via channel 40 to offset counter 41 and to display bit counter 42. A sign bit is included in the data loaded into multiplier 24 and is forwarded via channel 43 to Exclusive OR gate 44 and to offset counter 41. Y offset data is loaded into offset counter 41 via inputs 45. Offset counter 41 provides an output via channel 46 to Exclusive OR gate 44, which, in turn, provides an output via channel 47 to display bit counter 42. Display bit counter 42 has a plurality of inputs 48 adapted to receive digital data relating to the Y position of a line to be displayed and includes an enable input 49. An output 50 from counter 42 provides an advance input to offset counter 41. The output via channel 51 from counter 42 provides an input to digital-to-analog converter 53 which converts the digital data from counter 42 to an analog signal for processing via channel 54 on the deflection circuits of the cathode ray tube. Preferably, and as will be more fully understood hereinafter, offset counter 41 also provides an enable output via channel 55 to the video control.

In the operation of the circuit illustrated in FIG. 1, if it is desired that a line be displayed, an enable signal is applied to counter 10 via channel 14 so that data relating to the length of a line to be displayed may be loaded into counter 10 via inputs 11. This data may indicate a line longer than the width (X axis) or height (Y axis) of the display screen, or it may be shorter than thewidth or height of the display screen. Also, control 19 is enabled via channel 21 so that data relating to the rate at which the line is to be displayed (AL/AT) maY be loaded into counter 19 via inputs 20. The output from control 19 is impressed onto channel 23 to establish a line rate clock pulse series onto counter 10 and multipliers 16 and 24.

Data relating to the intended rate of advance of the X and Y axes display of the line are loaded into multipliers 16 and 24, respectively. Enable signals via channels 18 and 26 permit the loading of these data into the respective multipliers.

When SOL channel 13 is initiated, clock pulses from control 19 begin stepping through the count in counter 10 to produce enable pulse onto channel to X rate multiplier 16, Y rate multiplier 24 and live rate control 19. Control 19 produces clock pulses which are forwarded to multipliers l6 and 24 via channel 23. The pulse rate is multiplied in multiplier 16 by a factor determined by the advance rate loaded onto the multiplier to produce a series of clock pulses on channel 27 to offset counter 28 and to display bit counter 29 representative of the advance of display along the X axis. The pulses from counter 10 are also forwarded to Y rate multiplier 24 to be multiplied by a factor dependent upon the advance rate loaded into multiplier 24 to produce a second series of clock pulses on channel 40 to offset counter 41 and to display bit counter 42 representative of the advance of display along the Y axis.

The relative rates of clock pulses on channels 27 and 40 will determine the rates at which the display of a line on the cathode ray tube will advance. For example, if it is desired to display a line at an angle of 30 to the X axis, multiplier 16 is loaded with rate data via channel 17 to produce clock pulses on channel 27 having a rate greater than those on channel 40 to thereby advance the display at the desired 30 angle.

With reference to FIG. 2, assume that region 56 is the region of the display screen of the display device, and assume further that it'is desired to display a line having a slope at +30 from the X axis commencing at point 57. Data is loaded into display bit counters 29 and 42 concerning the initial X-Y position (X0, Y0) of the start point 57. As the clock pulses from multipliers 16 and 24 are impressed on display bit counters 29 and 42, respectively, the counts in counters 29 and 42 advance. Digital-to-analog converters 37 and 53 convert the counts in the respective counters to produce increasing voltages to the X and Y deflection circuits to advance the display along line 58 on the display. The rate of advance of the line in. both the X and Y directions is determined by the data loaded into the rate multipliers, as heretofore described.

The data supplied to the rate multipliers also includes a sign bit indicative of the direction of advance along a particular axis. The sign bit applied to a rate multiplier is forwarded via a respective channel 30 or 43 to Exclusive OR gates 31 and 44, respectively, to condition the respective. display counter to count positively or negatively. For example, a l sign bit on a channel might cause the respective counter to count positively, whereas an 0 bit on a channel 30 or 43 will condition the respective display counter to count negatively. Thus, and as shown in FIG. 3, if it is desired to display a line advancing along the X axis at -30", a l bit will be applied to channel 30 and an 0" bit will be applied to channel 43 so that the count in the display counter 29 increases with clock pulses from multiplier 16 while the count in display counter 42 decreases with clock pulses from multiplier 24. Hence, the display line will commence at start point 59 and advance along line 60 at an angle of 30 to the X axis.

The line will be displayed on the display screen for a length determined by data supplied to line length counter 10. If the length of the display line is less than the width of the display screen, counter 10 will count down, at the rate determined by the clock pulses from rate control 19, until the count preset in the counter (indicative of the length of the line) is counted out to zero. Thus, as shown in FIG. 3, the line will halt at point 61 due to the end of the count established for the line. If, however, the line to be displayed is longer than the width of the display screen, as shown in FIG. 2, when the display bit counter 29 reaches the maximum count indicative of the right edge of screen 56, display counter 29 provides a signal to offset counter 28 via channel 36 to step the count in counter 28 by 1. This signal is forwarded via video control channel 39 to turn off the video display, as will be more fully understood hereinafter.

Heretofore, it has been assumed that a single line is to be displayed. However, if it is desired to display a sweep, for example, data from a scan cycle of a radar sweep, line length counter 10 is biased to pass clock pulses at the rate established by rate control 19 without present line length.

Offset counters 28 and 41 are preloaded with data relating to whether the intended display is on or off screen. Heretofore, it has been assumed that the counts in counters 28 and 41 are such that the intended display is on screen and that the least significant bit of each count is a 1. However, when the display goes off screen, as sensed by the count in either counter 29 or 42, a signal is sent to the respective counter 28 or 41 via channel 36 or 50 to advance the binary count in that counter by l so that the least significant bit in that counter becomes a binary O. The presence of a binary 0 at the least significant bit position in a counter 28 or 41 is detected by Exclusive OR gate 31 or 44 to change signal supplied to the respective counter 29 or 42 to thereby reverse the change of the count in the display counter to reverse the direction of advance of the display.

FIG. 4 shows the effect of the continuous sweeping of the display generator according to the present invention. Assuming that both offset counters are threeposition binary counters and that both contain a count of 1 11 (a condition which indicates on screen dis play, as will be more fully described hereinafter), the least significant bit for both counts is a 1. Let it be assumed, for simplicity of explanation, that the display line is starting from point X0, Y0 on-screen and is advancing positively along both the X and Y axes. Thus, the line is displayed along line 62 until a full count is detected in the X display counter 29, at a point coincident with the right edge of display 56. When the line reaches point 63 at the right edge of display 56, the count in counter 29 is such as to indicate that the line has reached the right edge of display 56 and counter 29 forwards a signal to counter 28 to add l to the l l 1 count already in counter 28 to set counter 28 to 000.

Channels 39 and 55 from offset counters 28 and 41 are preferably connected to the video control circuits of the display to permit display of a line only when both counters contain a l l l binary set. For example, an AND gate (not shown) may be connected to channels 39 and 55 to operate the video circuits when all binary positions of counters 28 and 41 contain l binary signals. However, when counter 28 is reset to 000, the necessary condition for display isnot present. Thus, when the display line reaches an edge of the display region, the video is turned off. Further, the 0 least significant bit in offset counter 28 biases Exclusive OR gate 31 to change the sign bit delivered to display counter 29 thereby reversing the direction of advance of the apparent line (even though not displayed) in the X direction to bias the deflection circuits as shown by dashed line 64.

When the bias reaches the top edge of the display region, counter 42 detects a maximum count to thereby reset offset counter 41 to 000 thereby reversing the advance of the apparent display in the Y direction, as shown by dashed lines 65.

The process continues until the offset counters again reach a count of 111, thereby biasing on the video circuits to permit display. It is evident, therefore, that only one region of a sweep or scan is displayed. This feature enables viewing of a region of a scan of radar signals,thereby eliminating the display of unwanted data.

One feature of the invention resides in thefact that a sweep may be commenced at a point off screen. Thus, in P16. 5, a plurality of region 56, 56a, 56b, 56c, 56d and 56e are shown, but only data in region 56 is to be displayed. If a-display line commences off screen, for example, in region 56c at point 66, the count in offset counter 28 is preset to 101 f (indicating an offset by two regions in the X direction) and the count in offset counter 41 is preset at l (indicating an offset by one region in the Y direction). Since the Exclusive OR gates have the effect of reflecting a line when it is off screen by an odd number of regions (where a 0" is the least significant bit), it is evident that the portion of real line 67 in section 560 can be reflected about the Y axis to appear as line 67' in region 56b, commencing from point 66. Likewise, the line portion 67' and that portion of line 67 in region 56b can be reflected into region 56d about the X axis to appear as line 67 in region 56d, commencing from point 66". Likewise, the line portion 67" and that portion of line 67 in region 56d can be reflected into region 56 about the Y axis to appear as line 67" in region 56, commencing at point 66"].

Data concerning line 67 and 66 is applied directly to the rate multipliers 16 and 24 and to display counters 29 and 42. In addition, a 101 code is applied to the X offset counter 28 and a 1 10 code is applied to the Y offset counter 41. Since the line is advancing positively in both the X and Y directions, a 1 sign bit is applied to the rate multipliers. Since the least significant bit in the X offset counter is a l the initial X position of the deflection circuitry is unchanged. Thus, the X position of point 66 in region 56c is the same as the X position of point 66" in region 56. However, the 0 bit in the least significant position in Y offset counter 41 reverses the initial position data so the distance along the Y axis between points 66 and 66" and the X axis are the same, but the points lie on opposite sides of the X axis. Also, and as heretofore explained, the 0 bit in counter 41 causes a negative advance in the Y direction. Thus, bias line 67" advances positively along the X axis and negatively along the Y axis toward the right edge of region 56, where the X offset counter 28 steps l to 110 to reverse the direction of advance of the X bias. When line 67' reaches the lower edge of region 66, the Y offset counter 41 steps l to l l l to reverse the direction of the Y advance to positive, and finally when line 67"" reaches the left edge of region 56 the X offset counter steps by l to l l 1.

When both offset counters reach a l l 1 condition, as shown at point 69, the video circuits are operated via channels 39 and 55 ,to display line 67 as it passes through region 56, as heretofore described. When the line reaches the right edge of region 56, it would follow line 68 into the next adjacent region. However, X offset counter 28 steps 1 to 000 thereby turning off the video and reflecting the bias to follow line 68'.

With reference to FIG. 6 there is illustrated a character display generator according to the presently preferred embodiment of the present invention. The character display generator comprises an address memory having a plurality of inputs 81 adapted to be connected to a data processor for receiving a character code. Channels 82 connect the output of address memory 80 to the input of stroke counter 83, which in turn provides outputs via channels 84 to stroke memory 85. Stroke memory 85 contains binary data relating to the successive strokes to be taken for each character to be displayed. Thus, if a single character requires six consecutive strokes, the stroke memory will contain information as to each stroke for that character. Thus, the stroke memory contains stored data, in tabular program form, relating to each character so that by addressing a single character in the stroke memory, the various stroke data for all strokes may be read out in succession.

The output from stroke memory 85 is forwarded via channels 86 to stroke generator 87 which in turn produces a series of clock pulses on a selected basis for processing by X and Y counters 88 and 89. The output of X counter 88 is connected to digital-to-analog converter 90 to convert the digital signal to an analog signal for processing by the X video deflection circuits connected to output 91. The output of Y counter 89 is connected to digital-to-analog converter 92 to convert the digital signal to an analog signal for processing by the Y deflection circuits connected to output 93.

A character timing gate circuit 94 is provided for timing the stroke counter 83 and stroke generator 87 over the length of a single character. Circuit 94 has a first input 95 connected to the data processor for receiving a Start of Character (SOC) code to initiate operation of counter 83 and generator 87, and has a second input 95 connected to the last line from memory 85 for receiving an End of Character (EOC) code to halt operation of counter 83 and generator 87. A stroke advance channel 97 is connected from generator 87 to counter 83 to advance the count in counter 83 upon generation of each stroke.

In operation of the character generator illustrated in FIG. 6, and with reference to FIG. 7, let it be assumed that the character N is to be displayed on the display screen. A binary code, indicative of the character N, is received from the data processor via channel 81. The code selects an address code associated with the character from address memory 80. The address code selects that portion of memory 85 containing the data relating to the set of strokes associated with the character When the SOC character is received from the data processor, gate 94 initiates stroke counter 83 to select from memory 85 data concerning the first stroke of the character to be forwarded to stroke generator 87. Thus, to display the character N as shown in FIG. 6, and assuming the deflection circuits to be biased to point 103 on the screen, a code indicative of a 3 advance on the X axis and *3 advance on the Y axis is forwarded to generator 87 to cause the display bias to move to point 106. During this sweep, video circuits associated with the display device are biased off. When the deflection circuits are biased to point 106, the video circuits are operated via channel 104 and a code indicative of advance on the X axis and +3 advance on the Y axis is forwarded to generator 87 to cause 0 clock pulses to be forwarded to X counter 88 and 3n clock pulses to be forwarded to Y counter 89, where n is the number of clock pulses per unit of stroke. A sign bit indicative of advance is also forwarded to Y counter 89 to achieve a forward bias of the Y axis deflection circuits. Converters 90 and 92 convert the signals to analog signals to achieve the advance. Thus, a first line 100 is displayed on the display screen.

Upon completion of the first stroke, stroke generator 87 sends a pulse via advance channel 97 to stroke counter 83 to advance the count in counter 83 to the next position, thereby selecting the next stroke for the character. Memory 85 selects the next stroke data (eg X 0, Y +3) to cause display of line 101. The process continues until completion of the character. Thus, the third stroke data might be X 2, Y= 3; the fourth stroke data might be X 2, Y== 3; and the fifth and sixth stroke data each might be X 0 and Y= +3.

,llpo mple i ngfiths a t ilhe dqfles i n i cuits are, of course, biased to the point shown at 102. It is therefore desirable to bias the deflection circuitry to return to point 103. Memory sends an EOC character to gate 94 to halt further operation of stroke counter 83 and stroke generator 87, until another SOC character is received by gate 94. At the same time, the stroke generator causes counter 88 and 89 to reset the bias on the deflection circuitry back to point 103.

A more complex character might be displayed through selective operation of the video circuitry through memory 85. Thus, and as illustrated in FIG. 8 the character K might be displayed with the first stroke of X =-2 and Y=3 with video off, second and third stroke codes of X 0 and Y= +3 with video on; a fourth code of X +3, Y 0 with video biased off; a fifth stroke code of X -3, Y= --3 with video on; a sixth code of X +3, Y 3 with video on. An EOC character will bias the deflection circuits back to the point of origin.

As shown in FIGS. 7 and 8, the deflection circuits are biased back to the point of origin of the character. However, to display a plurality of characters, a character advance code (e.g.X =+6) may be provided to display successive characters.

The circuit illustrated in FIG. 6 may be combined with that shown in FIG. 1 by summing the signals present on channels 38 and 91 and imposing the result on the X axis video deflection circuit of a CRT and by summing the signals present on channels 54 and 93 and imposing the result on the Y axis. video deflection circuit. As a result, alpha-numeric data generated by the circuit shown in FIG. 6 may be displayed along a display line determined by the circuit shown in FIG. 1.

The sweep clock input to line length counter 10 may be eliminated if the clock rate for the line counter is established by the line rate control 19. Alternatively, the sweep clock may be used in lieu of the line rate control. Preferably, means (not shown) is provided for selectively adjusting the line rate data to control 19 so that the rate of display is advanced or retarded as selected by the operator.

The present invention thus provides a digital display generator capable of establishing display data, both on and off screen, by digital techniques. Thus, handling of display data is simplified, since the matching of attenuation of analog signals is not necessary, thereby providing a simpler, more effective technique for handling display data. The invention is particularly useful in connection with radar display applications wherein a single display is intended to view only selected regions of a scan.

This invention is not to be limited by the embodiments shown in the drawings and described in the description, which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims.

What is claimed is:

1. A display generator for generating deflection signals for operating on deflection circuitry of a display device for moving a visual representation generated by said display device in an area defined by a plurality of regions in first and second directions parallel to first and second mutually perpendicular axes respectively and said display device is operated to display only visual representations in selected regions, said apparatus comprising:

a. clock means producing clock pulses at a predetermined rate;

b. first pulse generator means selectively operable to produce first pulses at a rate representative of the rate of movement of said visual representation in said first direction;

c. second pulse generator means selectively operable to produce second pulses at a rate representative of the rate of movement of said visual representation in said second direction;

cl. said first and second pulse generator means each contains data respecting the selected increase or decrease of count in the respective first and second counter means; v

e. first counter means operable to maintain a first count representative of the position of said visual representation along said first axis;

f. second counter means operable to maintain a second count representative of the position of said visual representation along said second axis;

g. control means connected to said first and second pulse generator means to said first and second counter means and operable in response to said data for selectively increasing or decreasing said first count in said first counter means at the rate of said first pulses and for selectively increasing or decreasing said second count in said second counter means at the rate of said second pulses;

h. fourth counter means containing a predetermined count representative of the location of the region in which the visual representation is positioned, means connecting said first counter means to said fourth counter means to selectively increase or decrease the count insaid fourth counter means whenever the count in said first counter means indicates that the intended visual representation reaches a region edge which intersects said first axis, and means connecting said fourth counter means to said control means to reverse the alteration of counts in said first counter means whenever the count in said fourth counter means is changed, whereby said control means operates on said first counter means to reverse the alteration of count in said first counter means between increasing and decreasing count whenever the count in said first counter means is increased or decreased to a count indicative of a region edge intersecting said first axis; and

i. converter means connected to said first and second counter means for producing first and second analog signal representative of the value of said first and second counts respectively.

2. Apparatus according to claim 1 further including said first pulse generator comprising first multiplier means for storing information representative of the rate of movement of said visual display in said first direction, said first multiplier means being connected to said clock means to produce said first pulses at a rate representative of the product of said predetermined rate of said clock pulses and the rate established by the information stored in said first multiplier means; said second pulse generating means comprising second multiplier means for storing information representative of the rate of movement of said visual display in said second direc-.

tion, said second multiplier means being connected to said clock means to produce said second pulses at a rate representative of the product of said predetermined rate of said clock pulses and the rate established by the information stored in said second multiplier means.

3. Apparatus according to claim 2 further including input means connected to said first and second multiplier means for storing said information in the respective multiplier means.

4. Apparatus according to claim 2 further including means for selectively adjusting said predetermined rate of said clock pulses.

5. Apparatus according to claim 2 wherein said clock means further includes third counter means having an input for storing a count in said third counter means representative of a predetermined distance of move.- ment of said visual representation, said third counter means producing a predetermined number of said clock pulses at said predetermined rate, the number of said clock pulses being representative of the count stored in said third counter means.

6. Apparatus according to claim 1 further including fifth counter means'containing a predetermined count representative of the location of the region in which the visual representation is positioned, means connecting said second counter means to said fifth counter means to selectively increase or decrease the count in said fifth counter means, whenever the count in said second counter means indicates that the intended visual representation reaches a region edge which intersects said second axis, and means connecting said fifth counter means to said control means to reverse the alteration of counts in said second counter means whenever the count in said fifth counter means is changed, whereby said control means operates on said second counter means to reverse the alteration of count in said second counter means between increasing and decreasing count whenever the count in said second counter means is increased-or decreased to a count indicative of a region edge intersecting said second axis.

7. Apparatus according to claim 6 further including means connected to said fourth and fifth counter means for controlling said display device to prevent display of said visual representation whenever the count in said fourth and fifth counter means is such as to indicate said visual representation is in a region other than said selected quadrants.

8. Apparatus according to claim 6 wherein said control means comprises first Exclusive OR gate means having first and second inputs connected to said first pulse generator means and said fourth counter means, respectively, and an output connected to said first counter means, and second Exclusive OR gate means having first and second inputs connected to said second pulse generator means and said fifth counter means, respectively, and an output connected to said second counter means.

9. Apparatus according to claim 6 further including clock means producing clock pulses at a predetermined rate; said first pulse generator comprising first multiplier means for storing information representative of the rate of movement of said visual display in said first direction, said first multiplier means being connected to said clock means to produce said first pulses at a rate representative of the product of said predetermined rate of said clock pulses and the rate established by the information stored in said first multiplier means; said second pulse generator means comprising second multiplier means for storing information representative of the rate of movement of said visual display in said second direction, said second multiplier means being connected to said clock means to produce said second pulses at a rate representative of the product of said predetermined rate of said clock pulses and the rate established by the information stored in said second multiplier means.

10. Apparatus according to claim 8 further including input means connected to said first and second multiplier means for storing said information in the respective multiplier means.

11. Apparatus according to claim 8 further including means for selectively adjusting said predetermined rate of said clock pulses.

12. Apparatus according to claim 8 wherein said clock means further includes third counter means having an input for storing a count in said third counter means representative of a predetermineddistance of movement of said visual representative, said third counter means producing a predetermined number of said clock pulses at said predetermined rate, the number of said clock pulses being representative of the count stored in said third counter means.

13. Apparatus according to claim 1 further including character generator means for generating deflection signals for application to the deflection circuitry of said display device to display a character, said generator means comprising: storage means containing data concerning a plurality of strokes required to display each of a plurality of predetermined characters; address means adapted to receive selected character information concerning a character to be displayed, said address means responding to said character information to select data from said storage means corresponding to the selected character; generator means responsive to selected data from said storage means to generate first and second pulse trains of predetermined length determined by the data selected from said storage means; sixth counter means for selectively advancing or reducing its count in accordance with the length of said first pulse train and second counter means for selectively advancing or reducing its count in accordance with the length of said second pulse train; and second converter means connected to each of said first and second counter means for generating first and second analog signals each having a value representative of the count in the respective counter means.

14. Apparatus according to claim 13 further including stroke counter means connected to said address means for conditioning said storage means to forward to said generator means data related to the stroke of the character associated with the count in said stroke counter means, and means for advancing the count in said stroke counter means upon each generation of pulse trains by said generator means.

15. Apparatus according to claim 14 further including gate means responsive to the selection of data concerning the last stroke of a character to reset said stroke counter means.

16. Apparatus according to claim 13 further including second control means adapted to selectively operate video circuits associated with said display device.

17. Apparatus according to claim 16 wherein said second control means is selectively operated in accordance with data from said storage means.

18. Apparatus according to claim 1 further including storage means containing data concerning a plurality of strokes required to display each of a plurality of predetermined characters; and, address means adapted to receive selected character information concerning a character to be displayed, said address means responding to said character information to select data from said storage means corresponding to the selected character; said first and second pulse generator means responsive to selected data from said storage means to generate said respective first and second pulses as pulse trains of predetermined length determined by the data selected from said storage means.

19. Apparatus according to claim 18 further including stroke counter means connected to said address means for conditioning said storage means to forward to said generator means data related to the stroke of the character associated with the count in said stroke counter means, and means for advancing the count in said stroke counter means upon each generation of pulse trains by said generator means.

20. Apparatus according to'claim 19 further including gate means reponsive to the selection of data concerning the last stroke of a character to reset said stroke counter means.

21. Apparatus according to claim 18 further including control means adapted to selectively operate video circuits associated with said display device.

22. Apparatus according to claim 21 wherein said control means is selectively operated in accordance with data from said storage means. 

1. A display generator for generating deflection signals for operating on deflection circuitry of a display device for moving a visual representation generated by said display device in an area defined by a plurality of regions in first and second directions parallel to first and second mutually perpendicular axes respectively and said display device is operated to display only visual representations in selected regions, said apparatus comprising: a. clock means producing clock pulses at a predetermined rate; b. first pulse generator means selectively operable to produce first pulses at a rate representative of the rate of movement of said visual representation in said first direction; c. second pulse generator means selectively operable to produce second pulses at a rate representative of the rate of movement of said visual representation in said second direction; d. said first and second pulse generator means each contains data respecting the selected increase or decrease of count in the respective first and second counter means; e. first counter means operable to maintain a first count representative of the position of said visual representation along said first axis; f. secoNd counter means operable to maintain a second count representative of the position of said visual representation along said second axis; g. control means connected to said first and second pulse generator means to said first and second counter means and operable in response to said data for selectively increasing or decreasing said first count in said first counter means at the rate of said first pulses and for selectively increasing or decreasing said second count in said second counter means at the rate of said second pulses; h. fourth counter means containing a predetermined count representative of the location of the region in which the visual representation is positioned, means connecting said first counter means to said fourth counter means to selectively increase or decrease the count in said fourth counter means whenever the count in said first counter means indicates that the intended visual representation reaches a region edge which intersects said first axis, and means connecting said fourth counter means to said control means to reverse the alteration of counts in said first counter means whenever the count in said fourth counter means is changed, whereby said control means operates on said first counter means to reverse the alteration of count in said first counter means between increasing and decreasing count whenever the count in said first counter means is increased or decreased to a count indicative of a region edge intersecting said first axis; and i. converter means connected to said first and second counter means for producing first and second analog signal representative of the value of said first and second counts respectively.
 2. Apparatus according to claim 1 further including said first pulse generator comprising first multiplier means for storing information representative of the rate of movement of said visual display in said first direction, said first multiplier means being connected to said clock means to produce said first pulses at a rate representative of the product of said predetermined rate of said clock pulses and the rate established by the information stored in said first multiplier means; said second pulse generating means comprising second multiplier means for storing information representative of the rate of movement of said visual display in said second direction, said second multiplier means being connected to said clock means to produce said second pulses at a rate representative of the product of said predetermined rate of said clock pulses and the rate established by the information stored in said second multiplier means.
 3. Apparatus according to claim 2 further including input means connected to said first and second multiplier means for storing said information in the respective multiplier means.
 4. Apparatus according to claim 2 further including means for selectively adjusting said predetermined rate of said clock pulses.
 5. Apparatus according to claim 2 wherein said clock means further includes third counter means having an input for storing a count in said third counter means representative of a predetermined distance of movement of said visual representation, said third counter means producing a predetermined number of said clock pulses at said predetermined rate, the number of said clock pulses being representative of the count stored in said third counter means.
 6. Apparatus according to claim 1 further including fifth counter means containing a predetermined count representative of the location of the region in which the visual representation is positioned, means connecting said second counter means to said fifth counter means to selectively increase or decrease the count in said fifth counter means whenever the count in said second counter means indicates that the intended visual representation reaches a region edge which intersects said second axis, and means connecting said fifth counter means to said control means to reverse the alteration of counts in said second counTer means whenever the count in said fifth counter means is changed, whereby said control means operates on said second counter means to reverse the alteration of count in said second counter means between increasing and decreasing count whenever the count in said second counter means is increased or decreased to a count indicative of a region edge intersecting said second axis.
 7. Apparatus according to claim 6 further including means connected to said fourth and fifth counter means for controlling said display device to prevent display of said visual representation whenever the count in said fourth and fifth counter means is such as to indicate said visual representation is in a region other than said selected quadrants.
 8. Apparatus according to claim 6 wherein said control means comprises first Exclusive OR gate means having first and second inputs connected to said first pulse generator means and said fourth counter means, respectively, and an output connected to said first counter means, and second Exclusive OR gate means having first and second inputs connected to said second pulse generator means and said fifth counter means, respectively, and an output connected to said second counter means.
 9. Apparatus according to claim 6 further including clock means producing clock pulses at a predetermined rate; said first pulse generator comprising first multiplier means for storing information representative of the rate of movement of said visual display in said first direction, said first multiplier means being connected to said clock means to produce said first pulses at a rate representative of the product of said predetermined rate of said clock pulses and the rate established by the information stored in said first multiplier means; said second pulse generator means comprising second multiplier means for storing information representative of the rate of movement of said visual display in said second direction, said second multiplier means being connected to said clock means to produce said second pulses at a rate representative of the product of said predetermined rate of said clock pulses and the rate established by the information stored in said second multiplier means.
 10. Apparatus according to claim 8 further including input means connected to said first and second multiplier means for storing said information in the respective multiplier means.
 11. Apparatus according to claim 8 further including means for selectively adjusting said predetermined rate of said clock pulses.
 12. Apparatus according to claim 8 wherein said clock means further includes third counter means having an input for storing a count in said third counter means representative of a predetermined distance of movement of said visual representative, said third counter means producing a predetermined number of said clock pulses at said predetermined rate, the number of said clock pulses being representative of the count stored in said third counter means.
 13. Apparatus according to claim 1 further including character generator means for generating deflection signals for application to the deflection circuitry of said display device to display a character, said generator means comprising: storage means containing data concerning a plurality of strokes required to display each of a plurality of predetermined characters; address means adapted to receive selected character information concerning a character to be displayed, said address means responding to said character information to select data from said storage means corresponding to the selected character; generator means responsive to selected data from said storage means to generate first and second pulse trains of predetermined length determined by the data selected from said storage means; sixth counter means for selectively advancing or reducing its count in accordance with the length of said first pulse train and second counter means for selectively advancing or reducing its count in accordance with the length of Said second pulse train; and second converter means connected to each of said first and second counter means for generating first and second analog signals each having a value representative of the count in the respective counter means.
 14. Apparatus according to claim 13 further including stroke counter means connected to said address means for conditioning said storage means to forward to said generator means data related to the stroke of the character associated with the count in said stroke counter means, and means for advancing the count in said stroke counter means upon each generation of pulse trains by said generator means.
 15. Apparatus according to claim 14 further including gate means responsive to the selection of data concerning the last stroke of a character to reset said stroke counter means.
 16. Apparatus according to claim 13 further including second control means adapted to selectively operate video circuits associated with said display device.
 17. Apparatus according to claim 16 wherein said second control means is selectively operated in accordance with data from said storage means.
 18. Apparatus according to claim 1 further including storage means containing data concerning a plurality of strokes required to display each of a plurality of predetermined characters; and, address means adapted to receive selected character information concerning a character to be displayed, said address means responding to said character information to select data from said storage means corresponding to the selected character; said first and second pulse generator means responsive to selected data from said storage means to generate said respective first and second pulses as pulse trains of predetermined length determined by the data selected from said storage means.
 19. Apparatus according to claim 18 further including stroke counter means connected to said address means for conditioning said storage means to forward to said generator means data related to the stroke of the character associated with the count in said stroke counter means, and means for advancing the count in said stroke counter means upon each generation of pulse trains by said generator means.
 20. Apparatus according to claim 19 further including gate means reponsive to the selection of data concerning the last stroke of a character to reset said stroke counter means.
 21. Apparatus according to claim 18 further including control means adapted to selectively operate video circuits associated with said display device.
 22. Apparatus according to claim 21 wherein said control means is selectively operated in accordance with data from said storage means. 